1. Field of the Invention
The invention relates generally to heat exchanger for a motor vehicle. More specifically, the invention relates to a heat exchanger, such as an evaporator, having a distributor plate for improving the flow of refrigerant through the heat exchanger flow tubes.
2. Related Technology
Air conditioning systems for motor vehicles typically have a refrigeration cycle that circulates a refrigerant in order to control the temperature within the passenger compartment of the motor vehicle. During the refrigeration cycle, the refrigerant flows into a compressor, causing an increase in both pressure and temperature of the fluid. Exiting the compressor in a gaseous phase, the refrigerant is then condensed into a low-temperature liquid phase by a condenser. Next, the refrigerant flows through an expansion valve, which causes the refrigerant to expand into a low-pressure, low-temperature mixture of gas and liquid. The mixture of gas and liquid then flows into the evaporator and cools the passenger compartment to a desired temperature.
More specifically, after the refrigerant enters the evaporator it flows through a bank of thin, heat-transfer tubes that extend across the evaporator. The tubes are exposed to an influx of warm, ambient air that flows across the bank of tubes and absorbs heat therefrom; thereby causing all or most of the liquid portion of the refrigerant to evaporate into a gaseous state. The influx of air, having been sufficiently cooled, then enters the passenger compartment at the desired temperature.
Due to natural properties of fluids, evaporating liquids are able to absorb a certain amount of heat before increasing the temperature of the resulting gas. Therefore, to maximize the cooling effect of the air conditioner, and thus maximize the efficiency of the air conditioning system, it is advantageous for the liquid portion of the refrigerant entering the evaporator to be completely transformed into a gaseous state by the ambient air. One known technique for promoting phase-changes of the refrigerant is by increasing the amount of time that the refrigerant is exposed to the influx of air, such as by increasing the number of times that the refrigerant flows across the bank of heat-transfer tubes. However, this design increases the space required to house the evaporator within the motor vehicle.
As an alternative or an additional solution to the above-described design, the evaporator may have heat-exchange tubes with relatively small cross-sectional areas. However, smaller tubes typically cause uneven distribution of the gaseous-liquid mixture within the different tubes. More specifically, some of the tubes will tend to have an unproportionally high percentage of gas contained therein while other tubes will tend to have an unproportionally high percentage of liquid flowing therethrough. The uneven distribution of two-phase refrigerant may cause some or most of the liquid refrigerant to exit the tubes without evaporating, thereby decreasing the efficiency of the system.
It is therefore desirous to provide an air conditioning system that maintains a desired efficiency by equally distributing the liquid-phase refrigerant among the respective heat exchange tubes in the evaporator.